Zoom lens for projection and projection-type display apparatus

ABSTRACT

A zoom lens for projection includes a negative first group composed of two lenses, a second group composed of a positive lens, an aperture stop, a third group composed of a positive lens, a fourth group composed of a negative fourth-group-first lens, a fourth-group-second lens arranged in such a manner that a negative air lens is formed between the fourth-group-first lens and the fourth-group-second lens, and a positive fourth-group-third lens, and a fifth group composed of a positive lens having a convex surface facing the magnification side of the zoom lens, which are arranged in this order from the magnification side. Further, the following formula (1) is satisfied: 
       −0.6&lt;( R   72   +R   71 )/( R   72   −R   71 )&lt;0.6  (1), where
         R 71  is a radius of curvature of a magnification-side surface of the fourth-group-third lens, and   R 72  is a radius of curvature of a reduction-side surface of the fourth-group-third lens.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a 5-group 8-element zoom lens forprojection mountable on a projection-type display apparatus or the like,and to a projection-type display apparatus on which the zoom lens forprojection is mounted. In particular, the present invention relates to azoom lens for projection that magnifies rays of light carrying videoinformation output from a light valve, such as a transmissive orreflective liquid crystal display apparatus and a DMD (digitalmicromirror device) display apparatus, and projects the magnified raysof light onto a screen. Further, the present invention relates to aprojection-type display apparatus on which such a zoom lens forprojection is mounted.

2. Description of the Related Art

Projection-type display apparatuses using light valves, such as a liquidcrystal display apparatus and a DMD display apparatus, became widelyused in recent years. Especially, a projection-type display apparatususing three light valves corresponding to illumination light of RGBprimary colors is widely used. The projection-type display apparatususing three light valves modulates the illumination light of threeprimary colors by the three light valves for respective colors. Further,the modulated light is combined by a prism or the like, and the combinedlight is projected onto a screen through a projection lens to display animage.

Meanwhile, the sizes of the light valves became small, and theresolutions of the light valves became sharply higher. Further, aspersonal computers became widely used, a demand for the projection-typedisplay apparatus for use in presentation increased. Therefore, aprojection-type display apparatus having higher performance, a smallersize and a light weight is requested, because such a projection-typedisplay apparatus is conveniently usable, and easily settable. At thesame time, a projection lens having a smaller size and a light weight isstrongly requested.

As zoom lenses for projection that satisfy such requirements, zoomlenses for projection disclosed, for example, in Japanese UnexaminedPatent Publication No. 2004-109896 (Patent Document 1), JapaneseUnexamined Patent Publication No. 2004-279958 (Patent Document 2), andJapanese Unexamined Patent Publication No. 2005-156963 (Patent Document3) are known. The zoom lenses for projection disclosed in PatentDocuments 1 through 3 are composed of four or five lens groups, whichare seven or eight lenses.

However, in each of the zoom lenses for projection disclosed in PatentDocuments 1 through 3, the fourth lens group includes a cemented lens.The use of the cemented lens in the fourth lens group may beadvantageous to correction of chromatic aberrations, but it is difficultto correct especially an inclination of an image plane in an excellentmanner.

Therefore, the applicant of Japanese Patent Application No. 2010-127440,the priority of which is claimed in this patent application, proposed5-group zoom lenses for projection in Japanese Unexamined PatentPublication No. 2009-69539 (Patent Document 4) and Japanese UnexaminedPatent Publication No. 2009-69540 (Patent Document 5). In PatentDocuments 4 and 5, such an inclination of an image plane is corrected inan excellent manner by providing an air lens that functions as anegative lens in a fourth lens group, which is the fourth lens groupfrom the magnification side of the zoom lens.

However, in the zoom lenses for projection disclosed in Patent Documents4 and 5, a request for more excellent correction of various aberrationsincreased. Especially, more excellent correction of both sphericalaberrations and coma aberrations was requested.

SUMMARY OF THE INVENTION

In view of the foregoing circumstances, it is an object of the presentinvention to provide a five-group 8-element zoom lens for projectionhaving a smaller size and a lighter weight, and which can correctvarious aberrations, and especially both of spherical aberrations andcoma aberrations in a well-balanced excellent manner. Further, it isanother object of the present invention to provide a projection-typedisplay apparatus on which such a zoom lens for projection is mounted.

A zoom lens for projection according to a first aspect of the presentinvention is a zoom lens for projection comprising:

a first lens group having negative refractive power, and which iscomposed of two lenses;

a second lens group composed of a positive lens;

an aperture stop;

a third lens group composed of a positive lens;

a fourth lens group composed of three lenses of a fourth-group-firstlens, which is a negative lens, a fourth-group-second lens arranged insuch a manner that a negative air lens is formed between thefourth-group-first lens and the fourth-group-second lens, and afourth-group-third lens, which is a positive lens, and thefourth-group-first lens, the fourth-group-second lens and thefourth-group-third lens being arranged in this order from themagnification side of the zoom lens; and

a fifth lens group composed of a positive lens having a convex surfacefacing the magnification side, and the first lens group, the second lensgroup, the aperture stop, the third lens group, the fourth lens group,and the fifth lens group being arranged from the magnification side inthe order mentioned above,

wherein the following formula (1) is satisfied:

−0.6<(R ₇₂ +R ₇₁)/(R ₇₂ −R ₇₁)<0.6  (1), where

R₇₁ is a radius of curvature of a magnification-side surface of thefourth-group-third lens, and

R₇₂ is a radius of curvature of a reduction-side surface of thefourth-group-third lens.

A zoom lens for projection according to a second aspect of the presentinvention is a zoom lens for projection comprising:

a first lens group having negative refractive power, and which iscomposed of two lenses;

a second lens group composed of a positive lens;

an aperture stop;

a third lens group composed of a positive lens;

a fourth lens group composed of three lenses of a fourth-group-firstlens, which is a negative lens, a fourth-group-second lens arranged insuch a manner that a negative air lens is formed between thefourth-group-first lens and the fourth-group-second lens, and afourth-group-third lens, which is a positive lens, and thefourth-group-first lens, the fourth-group-second lens and thefourth-group-third lens being arranged in this order from themagnification side of the zoom lens; and

a fifth lens group composed of a positive lens having a convex surfacefacing the magnification side, and the first lens group, the second lensgroup, the aperture stop, the third lens group, the fourth lens group,and the fifth lens group being arranged from the magnification side inthe order mentioned above,

wherein the following formulas (2) and (3) are satisfied:

−0.85<(R ₇₂ +R ₇₁)/(R ₇₂ −R ₇₁)<0.85  (2); and

−6.0<f ₄ /f ₅  (3), where

R₇₁ is a radius of curvature of a magnification-side surface of thefourth-group-third lens,

R₇₂ is a radius of curvature of a reduction-side surface of thefourth-group-third lens,

f₄ is a focal length of the fourth lens group, and

f₅ is a focal length of the fifth lens group.

A zoom lens for projection according to a third aspect of the presentinvention is a zoom lens for projection comprising:

a first lens group having negative refractive power, and which iscomposed of two lenses;

a second lens group composed of a positive lens;

an aperture stop;

a third lens group composed of a positive lens;

a fourth lens group composed of three lenses of a fourth-group-firstlens, which is a negative lens, a fourth-group-second lens arranged insuch a manner that a negative air lens is formed between thefourth-group-first lens and the fourth-group-second lens, and afourth-group-third lens, which is a positive lens, and thefourth-group-first lens, the fourth-group-second lens and thefourth-group-third lens being arranged in this order from themagnification side of the zoom lens; and

a fifth lens group composed of a positive lens having a convex surfacefacing the magnification side, and the first lens group, the second lensgroup, the aperture stop, the third lens group, the fourth lens group,and the fifth lens group being arranged from the magnification side inthe order mentioned above,

wherein the following formulas (4) and (5) are satisfied:

−6.0<fn/fw<−2.0  (4); and

−11.0<f ₄ /f ₂  (5), where

fn is a focal length of the negative air lens,

fw is a focal length of the entire system of the zoom lens at a wideangle end,

f₂ is a focal length of the second lens group, and

f₄ is a focal length of the fourth lens group.

A zoom lens for projection according to a fourth aspect of the presentinvention is a zoom lens for projection comprising:

a first lens group having negative refractive power, and which iscomposed of two lenses;

a second lens group composed of a positive lens;

an aperture stop;

a third lens group composed of a positive lens;

a fourth lens group composed of three lenses of a fourth-group-firstlens, which is a negative lens, a fourth-group-second lens arranged insuch a manner that a negative air lens is formed between thefourth-group-first lens and the fourth-group-second lens, and afourth-group-third lens, which is a positive lens, and thefourth-group-first lens, the fourth-group-second lens and thefourth-group-third lens being arranged in this order from themagnification side of the zoom lens; and

a fifth lens group composed of a positive lens having a convex surfacefacing the magnification side, and the first lens group, the second lensgroup, the aperture stop, the third lens group, the fourth lens group,and the fifth lens group being arranged from the magnification side inthe order mentioned above,

wherein the following formula (6) is satisfied:

−24.0<f ₄ /fw<−6.0  (6), where

fw is a focal length of the entire system of the zoom lens at a wideangle end, and

f₄ is a focal length of the fourth lens group.

In the zoom lens for projection according to any one of aspects of thepresent invention, it is desirable that at least a surface of themagnification-side lens of the two lenses in the first lens group isaspheric, and that the reduction-side lens of the two lenses in thefirst lens group has a concave surface facing the reduction side of thezoom lens. Further, it is desirable that the positive lens in the secondlens group has a convex surface facing the magnification side, and thatthe positive lens in the third lens group has a convex surface facingthe magnification side. Further, it is desirable that thefourth-group-first lens of the three lenses in the fourth lens group hasa concave surface facing the magnification side, and that thefourth-group-third lens of the three lenses in the fourth lens group hasa convex surface facing the reduction side.

In the zoom lens for projection according to any one of aspects of thepresent invention, it is desirable that at least one of the followingformulas (7) and (8) is satisfied:

3.0<|f _(1A) /fw|  (7); and

−20.0<fn/fw<−0.5  (8), where

fw is a focal length of the entire system of the zoom lens at a wideangle end,

f_(1A) is a focal length of the magnification-side lens in the firstlens group, and

fn is a focal length of the negative air lens.

In the zoom lens for projection according to any one of aspects of thepresent invention, it is desirable that the second lens group, the thirdlens group, and the fourth lens group move in the direction of anoptical axis when magnification is changed.

In this case, it is desirable that the second lens group and the thirdlens group move as one body when magnification is changed.

Further, when the second lens group and the third lens group arestructured in such a manner to move as one body during changingmagnification, it is desirable that focusing is performed by moving thefirst lens group in the direction of an optical axis.

In the zoom lens for projection according to any one of aspects of thepresent invention, it is desirable that the negative air lens has adouble-convex shape.

Further, in the zoom lens for projection according to any one of aspectsof the present invention, it is desirable that the fourth lens groupincludes a lens having at least one aspheric surface.

Further, a projection-type display apparatus of the present invention isa projection-type display apparatus comprising:

a light source;

a light valve;

an illumination optical system that guides rays of light output from thelight source to the light valve; and

a zoom lens for projection according to any one of aspects of thepresent invention,

wherein the light valve optically modulates the rays of light outputfrom the light source, and

wherein the zoom lens for projection projects the modulated rays oflight onto a screen.

The term “magnification side” refers to a projected-side (screen side),and for convenience, the screen side is called as a magnification sidealso in reduction projection. Further, the term “reduction side” refersto an original image display area side (light valve side), and forconvenience, the light valve side is called as a reduction side also inreduction projection.

The zoom lenses for projection according to the first through fourthaspects of the present invention and the projection-type displayapparatuses using the zoom lenses for projection have specificstructures that make the following actions and effects are achievable.

Specifically, the zoom lens for projection according to the first aspectof the present invention and the projection-type display apparatus usingthe zoom lens for projection satisfy the formula (1). Therefore, arelationship between the radii of curvature of the two surfaces of thefourth-group-third lens in the fourth lens group is regulated in apredetermined range. Consequently, it is possible to correct variousaberrations, such as coma aberrations and spherical aberrations, in anexcellent manner.

Further, the zoom lens for projection according to the second aspect ofthe present invention and the projection-type display apparatus usingthe zoom lens for projection satisfy the formula (2). Therefore, arelationship between the radii of curvature of the two surfaces of thefourth-group-third lens in the fourth lens group is regulated in apredetermined range. Consequently, it is possible to correct variousaberrations, such as coma aberrations and spherical aberrations, in anexcellent manner. At the same time, the zoom lens for projectionaccording to the second aspect of the present invention and theprojection-type display apparatus using the zoom lens for projectionsatisfy the formula (3). Therefore, a relationship between the power ofthe fourth lens group and the power of the fifth lens group is regulatedin a predetermined range. Especially, when the fourth lens group hasnegative power, the power of the fifth lens group is controlled at apredetermined value or lower. Therefore, all aberrations are correctedin an excellent manner.

Further, the zoom lens for projection according to the third aspect ofthe present invention and the projection-type display apparatus usingthe zoom lens for projection satisfy the formula (4). Therefore, thepower of the air lens formed between the fourth-group-first lens and thefourth-group-second lens is regulated in a predetermined range.Consequently, it is possible to correct aberrations, especiallyaberrations related to an image plane in the sagittal direction and comaaberrations, in an excellent manner. At the same time, the zoom lens forprojection according to the third aspect of the present invention andthe projection-type display apparatus using the zoom lens for projectionsatisfy the formula (5). Therefore, the power of the fifth lens groupdoes not become too strong. Consequently, all aberrations are correctedin an excellent manner.

Further, the zoom lens for projection according to the fourth aspect ofthe present invention and the projection-type display apparatus usingthe zoom lens for projection satisfy the formula (6). Therefore, thepower of the fourth lens group is regulated in a predetermined range,and that is advantageous to correction of various aberrations. Further,it is possible to reduce the size of the projection-type displayapparatus, and to increase the angle of view of the zoom lens forprojection.

Further, in the zoom lenses for projection according to the firstthrough fourth aspects of the present invention and the projection-typedisplay apparatuses using the zoom lenses, the zoom lens for projectionis composed of five lens groups, which are eight lenses. The simplestructure of the zoom lens for projection makes it possible to easilyreduce the size and the weight of the zoom lens and those of theprojection-type display apparatus. Further, the fourth lens group iscomposed of three lenses of the fourth-group-first lens, thefourth-group-second lens and the fourth-group-third lens, and a negativeair lens is formed between the fourth-group-first lens and thefourth-group-second lens. Therefore, it is possible to correct variousaberrations, such as an inclination of an image plane, by adjusting theshape of the air lens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 1 of the present invention at a wide angle end(WIDE) and a telephoto end (TELE);

FIG. 2 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 2 of the present invention at a wide angle end(WIDE) and a telephoto end (TELE);

FIG. 3 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 3 of the present invention at a wide angle end(WIDE) and a telephoto end (TELE);

FIG. 4 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 4 of the present invention at a wide angle end(WIDE) and a telephoto end (TELE);

FIG. 5 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 5 of the present invention at a wide angle end(WIDE) and a telephoto end (TELE);

FIGS. 6Ai, 6Aii, 6Aiii and 6Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 1 at a wide angle end (WIDE);

FIGS. 6Bi, 6Bii, 6Biii and 6Biv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 1 at a telephoto end (TELE);

FIGS. 7 i, 7 ii, 7 iii, 7 iv and 7 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 1 at a wide angleend (WIDE);

FIGS. 8 i, 8 ii, 8 iii, 8 iv and 8 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 1 at a telephotoend (TELE);

FIGS. 9Ai, 9Aii, 9Aiii and 9Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 2 at a wide angle end (WIDE);

FIGS. 9Bi, 9Bii, 9Biii and 9Biv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 2 at a telephoto end (TELE);

FIGS. 10 i, 10 ii, 10 iii, 10 iv and 10 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 2 at a wide angleend (WIDE);

FIGS. 11 i, 11 ii, 11 iii, 11 iv and 11 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 2 at a telephotoend (TELE);

FIGS. 12Ai, 12Aii, 12Aiii and 12Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 3 at a wide angle end (WIDE);

FIGS. 12Bi, 12Bii, 12Biii and 12Biv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 3 at a telephoto end (TELE);

FIGS. 13 i, 13 ii, 13 iii, 13 iv and 13 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 3 at a wide angleend (WIDE);

FIGS. 14 i, 14 ii, 14 iii, 14 iv and 14 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 3 at a telephotoend (TELE);

FIGS. 15Ai, 15Aii, 15Aiii and 15Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 4 at a wide angle end (WIDE);

FIGS. 15Bi, 15Bii, 15Biii and 15Biv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 4 at a telephoto end (TELE);

FIGS. 16 i, 16 ii, 16 iii, 16 iv and 16 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 4 at a wide angleend (WIDE);

FIGS. 17 i, 17 ii, 17 iii, 17 iv and 17 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 4 at a telephotoend (TELE);

FIGS. 18Ai, 18Aii, 18Aiii and 18Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 5 at a wide angle end (WIDE);

FIGS. 18Bi, 18Bii, 18Biii and 18Biv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 5 at a telephoto end (TELE);

FIGS. 19 i, 19 ii, 19 iii, 19 iv and 19 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 5 at a wide angleend (WIDE);

FIGS. 20 i, 20 ii, 20 iii, 20 iv and 20 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 5 at a telephotoend (TELE); and

FIG. 21 is a schematic diagram illustrating the configuration of aprojection-type display apparatus according to an embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to drawings. FIG. 1 illustrates a zoom lens for projectionaccording to an embodiment of the present invention (a zoom lens forprojection in Example 1 is used as an example). The zoom lens forprojection illustrated in FIG. 1 is composed of first lens group G₁having negative refractive power, and which is composed of two lenses,second lens group G₂ composed of a positive lens, an aperture stop 3,third lens group G₃ composed of a positive lens, fourth lens group G₄composed of three lenses of a fourth-group-first lens (lens L₅ in FIG.1), which is a negative lens, a fourth-group-second lens (lens L₆ inFIG. 1) arranged in such a manner that a negative air lens is formedbetween the fourth-group-first lens (lens L₅) and thefourth-group-second lens (lens L₆), and a fourth-group-third lens (lensL₇ in FIG. 1), which is a positive lens, and the fourth-group-firstlens, the fourth-group-second lens and the fourth-group-third lens(lenses L₅, L₆, L₇) being arranged in this order from the magnificationside of the zoom lens, and fifth lens group G₅ composed of a positivelens having a convex surface facing the magnification side. The firstlens group G₁, the second lens group G₂, the aperture stop 3, the thirdlens group G₃, the fourth lens group G₄, and the fifth lens group G₅ arearranged from the magnification side in the order mentioned above.Further, the reduction side of the zoom lens for projection istelecentric. A glass block (including a filter portion) 2, which ismainly a color combination prism, and an image display plane 1 of alight valve, such as a liquid crystal display panel, are arranged on thedownstream side of the zoom lens for projection. In FIG. 1, line Zrepresents an optical axis.

In Examples 1 through 5, the lens groups G₁ through G₅ are basicallystructured as described below. Specifically, the first lens group G₁ iscomposed of first lens L₁ and second lens L₂, which are arranged in thisorder from the magnification side of the zoom lens for projection. Thefirst lens L₁ is an aspheric lens (made of plastic), and at least asurface of the first lens L₁ is aspheric. The second lens L₂ is anegative lens having a concave surface facing the reduction side of thezoom lens for projection. The second lens group G₂ consists of thirdlens L₃, in other words, the second lens group G₂ is composed of onlythird lens L₃. The third lens L₃ is a positive lens having a convexsurface facing the magnification side. The third lens group G₃ consistsof fourth lens L₄, in other words, the third lens group G₃ is composedof only fourth lens L₄. The fourth lens L₄ is a positive lens having aconvex surface facing the magnification side. The fourth lens group G₄is composed of three lenses of fifth lens L₅, sixth lens L₆, and seventhlens L₇, which are arranged in this order from the magnification side.The fifth lens L₅ is a negative lens having a concave surface facing themagnification side. The sixth lens L₆ is arranged in such a manner thata negative air lens is formed between the fifth lens L₅ and the sixthlens L₆. The seventh lens L₇ is a positive lens having a convex surfacefacing the reduction side. The fourth lens group G₄, as a whole, haspositive refractive power (Example 5) or negative refractive power(Examples 1 through 4). It is desirable that the fourth lens group G₄includes a lens having at least an aspheric surface. Aberrations arecorrected in an excellent manner by an aspheric lens having a small lensdiameter. Further, the fifth lens group G₅ consists of eighth lens L₈,in other words, the fifth lens group G₅ is composed of only eighth lensL₈. The eighth lens L₈ is a positive lens having a convex surface facingthe magnification side. Since the zoom lens for projection is structuredin this manner, a negative air lens (double-convex shape in thefollowing examples) Ln is formed between the fifth lens L₅ and the sixthlens L₆ in the fourth lens group G₄.

Since the negative air lens Ln is formed between the fifth lens L₅ andthe sixth lens L₆ in the fourth lens group G₄, it is possible to correctan inclination of an image plane.

When the negative air lens Ln has a double-convex shape, the correctionfunction of the negative air lens Ln is further improved.

Further, it is desirable that the third lens group G₃ and the aperturestop 3 (a mask may be used) move as one body during zooming(corresponding to Examples 1 through 5).

As described above, the zoom lens for projection according to anembodiment of the present invention is a so-called negative-lead-typezoom lens. Therefore, it is possible to easily increase the projectionangle, and to ensure an appropriate length of back focus.

Further, the zoom function of the zoom lens for projection according toan embodiment of the present invention is achievable by moving threelens groups (in Examples 1 through 5, the second lens group G₂, thethird lens group G₃, and the fourth lens group G₄) in the direction ofan optical axis when magnification is changed. Since the three lensgroups, namely, the second lens group G₂, the third lens group G₃, andthe fourth lens group G₄ are movable lens groups, aberrations arecorrected in a more excellent manner. In this case, when the second lensgroup G₂ and the third lens group G₃ move as one body, it is possible tosimplify a drive mechanism of the zoom lens for projection. Further, itis possible to correct aberrations in a more excellent manner.

Further, it is desirable that all of the movable lens groups move towardthe magnification side when magnification is changed from a wide angleend to a telephoto end. In the embodiment of the present invention, itis possible to set a higher variable magnification ratio by structuringthe zoom lens for projection in such a manner.

This means that the position of each of the movable lens groups at atelephoto end is set on the magnification side of the position of therespective movable lens groups at a wide angle end. Therefore, any ofthe movable lens groups may temporarily move to the reduction side in amiddle range of variable magnification.

Further, it is desirable that focusing is performed by moving the firstlens group G₁ in the direction of the optical axis.

Alternatively, a different lens group may be moved for focusing.

A zoom lens for projection according to a first embodiment of thepresent invention satisfies the following formula (1):

−0.6<(R ₇₂ +R ₇₁)/(R ₇₂ −R ₇₁)<0.6  (1), where

R₇₁ is a radius of curvature of a magnification-side surface of theseventh lens L₇ (fourth-group-third lens), and

R₇₂ is a radius of curvature of a reduction-side surface of the seventhlens L₇ (fourth-group-third lens).

Further, a zoom lens for projection according to a second embodiment ofthe present invention satisfies the following formulas (2) and (3):

−0.85<(R ₇₂ +R ₇₁)/(R ₇₂ −R ₇₁)<0.85  (2); and

−6.0<f ₄ /f ₅  (3), where

R₇₁ is a radius of curvature of a magnification-side surface of theseventh lens L₇ (fourth-group-third lens),

R₇₂ is a radius of curvature of a reduction-side surface of the seventhlens L₇ (fourth-group-third lens),

f₄ is a focal length of the fourth lens group G₄, and

f₅ is a focal length of the fifth lens group G₅.

Further, a zoom lens for projection according to a third embodiment ofthe present invention satisfies the following formulas (4) and (5):

−6.0<fn/fw<−2.0  (4); and

−11.0<f ₄ /f ₂  (5), where

fn is a focal length of negative air lens Ln,

fw is a focal length of the entire system of the zoom lens at a wideangle end,

f₂ is a focal length of the second lens group G₂, and

f₄ is a focal length of the fourth lens group G₄.

Further, a zoom lens for projection according to a fourth embodiment ofthe present invention satisfies the following formula (6):

−24.0<f ₄ /fw<−6.0  (6), where

fw is a focal length of the entire system of the zoom lens at a wideangle end, and

f₄ is a focal length of the fourth lens group G₄.

Further, in any one of the embodiments of the present invention, it isdesirable that at least one of the following formulas (7) and (8) issatisfied:

3.0<|f _(1A) /fw|  (7); and

−20.0<fn/fw<−0.5  (8), where

fw is a focal length of the entire system of the zoom lens at a wideangle end,

f_(1A) is a focal length of the first lens L₁ in the first lens groupG₁, and

fn is a focal length of negative air lens Ln.

Next, the technical meanings of the formulas (1) through (8) will bedescribed.

In the formulas (1) and (2), the sum of the radii of curvature of thetwo surfaces of the seventh lens L₇, which is the most-reduction-sidelens in the fourth lens group G₄, is divided by the difference betweenthe radii of curvature of the two surfaces of the seventh lens L₇. Theformulas (1) and (2) define conditions for correcting sphericalaberrations and coma aberrations in an excellent manner. Specifically,when the value of (R₇₂+R₇₁)/(R₇₂−R₇₁) exceeds the upper limit defined bythe formula (1) or (2), coma aberrations become worse. When the value of(R₇₂+R₇₁)/(R₇₂−R₇₁) is lower than the lower limit defined by the formula(1) or (2), spherical aberrations become worse.

Therefore, it is more desirable that the following formula (1′) issatisfied instead of the formula (1):

−0.2<(R ₇₂ +R ₇₁)/(R ₇₂ −R ₇₁)<0.2  (1′).

Further, it is even more desirable that the following formula (1″) issatisfied:

−0.1<(R ₇₂ +R ₇₁)/(R ₇₂ −R ₇₁)<0.1  (1″).

In the formula (3), the focal length of the fourth lens group G₄ isdivided by the focal length of the fifth lens group G₅. The formula (3)defines the range of the value of f₄/f₅ for correcting aberrations, as awhole, in an excellent manner. Specifically, when the value of f₄/f₅ islower than the lower limit defined by the formula (3), the power of thefifth lens group G₅ becomes too strong, and it becomes difficult tocorrect aberrations, as a whole, in an excellent manner.

Further, the formula (4) defines the range of the power of the air lensthat can correct aberrations in an excellent manner. Specifically, whenthe value of fn/fw is lower is lower than the lower limit defined by theformula (4), it becomes difficult to correct aberrations, especially,curvature of field in sagittal direction. When the value of fn/fwexceeds the upper limit defined by the formula (4), it becomes difficultto correct aberrations, especially, coma aberrations.

Therefore, it is desirable that the following formula (4′) is satisfiedinstead of the formula (4):

−5.0<fn/fw<−2.0  (4′).

In the formula (5), the focal length of the fourth lens group G₄ isdivided by the focal length of the second lens group G₂. The formula (5)defines the range of the value of f₄/f₂ for correcting aberrations, as awhole, in an excellent manner. Specifically, when the value of f₄/f₂ islower than the lower limit defined by the formula (5), the power of thesecond lens group G₂ becomes too strong, and it becomes difficult tocorrect aberrations, as a whole, in an excellent manner.

Therefore, it is more desirable that the following formula (5′) issatisfied instead of the formula (5):

−8.0<f ₄ /f ₂<0.0  (5′).

Further, it is even more desirable that the following formula (5″) issatisfied:

−7.0<f ₄ /f ₂<−3.0  (5″).

Further, the formula (6) defines the power of the fourth lens group G₄.The formula (6) defines conditions to be applied when the fourth lensgroup G₄ has negative power. When the value of f₄/fw is lower than thelower limit defined by the formula (6), the power of the fourth lensgroup G₄ is too strong, and it becomes difficult to correct aberrations.When the value of f₄/fw exceeds the upper limit defined by the formula(6), the power of the fourth lens group G₄ is too weak, and it becomesdifficult to widen the angle of view.

Therefore, it is desirable that the following formula (6′) is satisfiedinstead of the formula (6):

−15.0<f ₄ /fw<−7.0  (6′).

Further, the formula (7) defines the power of the first lens L₁, whichis the magnification-side lens in the first lens group G₁. The formula(7) defines conditions for correction aberrations, as a whole, in anexcellent manner. Specifically, when the value of |f_(1A)/fw| is lowerthan the lower limit defined by the formula (7), the power of the firstlens L₁, which is an aspheric lens, becomes strong. Especially, when theaspheric lens is made of plastic, a fluctuation of aberrations caused bya fluctuation of temperature becomes excessive.

Therefore, it is more desirable that the following formula (7′) issatisfied instead of the Formula (7):

5.0<|f _(1A) /fw|<20.0  (7′).

Further, it is even more desirable that the following formula (7″) issatisfied:

7.0<|f _(1A) /fw|<15.0  (7″).

Further, the formula (8) defines the power of the air lens Ln in thefourth lens group G₄. The formula (8) defines conditions for correctingespecially coma aberration and sagittal flare in an excellent manner.Specifically, when the value of fn/fw is lower than the lower limitdefined by the formula (8), it becomes difficult to correct sagittalflare. When the value of fn/fw exceeds the upper limit defined by theformula (8), it becomes difficult to correct coma aberrations.

Therefore, it is more desirable that the following formula (8′) issatisfied instead of the formula (8):

−10.0<fn/fw<−1.0  (8′).

Further, it is even more desirable that the following formula (8″) issatisfied:

−5.0<fn/fw<−2.0  (8″).

In each of the following examples, the zoom lens for projection includesan aspheric lens. The shape of the aspheric surface of the aspheric lensis represented by the following aspheric surface equation:

$\begin{matrix}{{Z = {\frac{Y^{Z}/R}{1 + \sqrt{1 - {K \times {Y^{Z}/R^{2}}}}} + {\sum\limits_{i = 3}^{10}{A_{i}Y^{i}}}}},} & \lbrack {{EQUATION}\mspace{14mu} 1} \rbrack\end{matrix}$

where

Z: length of a perpendicular from a point on an aspheric surface, thepoint away from an optical axis by distance Y, to flat plane (flat planeperpendicular to the optical axis) in contact with the vertex of theaspheric surface,

Y: distance from the optical axis,

R: a radius of curvature of the aspheric surface in the vicinity of theoptical axis,

K: eccentricity, and

A_(i): aspheric coefficient (i=3 through 10).

Next, with reference to FIG. 21, an example of a projection-type displayapparatus on which the aforementioned zoom lens for projection ismounted will be described. A projection-type display apparatus 30,illustrated in FIG. 21, includes transmissive liquid crystal panels 11a, 11 b, 11 c, as light valves. The projection-type display apparatus 30uses, as the zoom lens 10 for projection, the zoom lens for projectionaccording to the aforementioned embodiments of the present invention.Further, an integrator (not illustrated), such as a fly's eyeintegrator, is arranged between a light source 15 and a dichroic mirror12. White light output from the light source 15 enters, through anillumination optical unit, liquid crystal panels 11 a through 11 c,which correspond to rays of light of three colors (G light, B light andR right), respectively, and is optically modulated. The modulated lightof three colors is combined together by a cross dichroic prism 14, andprojected onto a screen, which is not illustrated, by the zoom lens 10for projection. The projection-type display apparatus 30 includesdichroic mirrors 12, 13 for separating colors, a cross-dichroic prism 14for combining colors, and condenser lenses 16 a, 16 b, 16 c, and totalreflection mirrors 18 a, 18 b, 18 c. Since the projection-type displayapparatus according to an embodiment of the present invention uses thezoom lens for projection according to an embodiment of the presentinvention, it is possible to reduce the size, the weight and theproduction cost of the apparatus while achieving high variablemagnification. Further, it is possible to maintain high opticalperformance.

It is not necessary that the zoom lens for projection of the presentinvention is used as a zoom lens for projection in a projection-typedisplay apparatus using transmissive liquid crystal panels or the like.The zoom lens for projection of the present invention may be used as azoom lens for projection in an apparatus using a different lightmodulation means, such as reflective liquid crystal display panels and aDMD.

EXAMPLES

The zoom lens for projection of the present invention will be furtherdescribed by using specific examples.

Example 1

As described already, the zoom lens for projection in Example 1 isstructured as illustrated in FIG. 1. Specifically, the zoom lens forprojection in Example 1 is composed of first lens group G₁ havingnegative refractive power, second lens group G₂, an aperture stop 3,third lens group G₃, fourth lens group G₄ having negative refractivepower, and fifth lens group G₅, which are arranged in this order fromthe magnification side of the zoom lens for projection. The first lensgroup G₁ is composed of first lens L₁ and second lens L₂, which arearranged in this order from the magnification side. The first lens L₁ isan aspheric lens (made of plastic), and both surfaces of the first lensL₁ are aspheric. The second lens L₂ is a double-concave lens. The secondlens group G₂ consists of third lens L₃, which is a double-convex lens,in other words, the second lens group G₂ is composed of only the thirdlens L₃. The third lens group G₃ consists of fourth lens L₄, which is adouble-convex lens. The fourth lens group G₄ is composed of three lensesof fifth lens L₅, sixth lens L₆ and seventh lens L₇, which are arrangedin this order from the magnification side. The fifth lens L₅ is adouble-concave lens. The sixth lens L₆ is arranged in such a manner thatnegative air lens (double-convex shape) Ln is formed between the fifthlens L₅ and the sixth lens L₆. The sixth lens L₆ has a positive meniscusshape having a concave surface facing the magnification side. Theseventh lens L₇ is a double-convex lens. The fifth lens group G₅consists of eighth lens L₈, which is a plano-convex lens having a convexsurface facing the magnification side. Further, the reduction side ofthe zoom lens for projection is telecentric. A glass block (including afilter portion) 2, which is mainly a color combination prism, and animage display plane 1 of a light valve, such as a liquid crystal displaypanel, are arranged on the downstream side of the zoom lens forprojection. In FIG. 1, line Z represents an optical axis.

When magnification is changed, the second lens group G₂, the third lensgroup G₃ and the fourth lens group G₄ move toward the magnification sideduring zooming from a wide angle end to a telephoto end. Further, thesecond lens group G₂ and the third lens group G₃ move as one body.Further, the aperture stop 3 also moves together with the second lensgroup G₂ and the third lens group G₃, as one body. Further, a mask maybe arranged together with the aperture stop 3, instead of arranging theaperture stop 3 alone.

Further, focusing is performed by moving the first lens group G₁ in thedirection of the optical axis Z.

The upper section of Table 1 shows the radius of curvature R (mm) ofeach lens surface in Example 1, the center thickness of each lens andair space between lenses D (mm), and refractive index N_(d) and the Abbenumber ν_(d) of each lens for d-line. In Table 1 and Tables 2 through 6,which will be described later, surface numbers corresponding to thevalues of R, D, N_(d), and ν_(d) sequentially increase from themagnification side.

Further, the top line of Table 1 shows focal length f, back focus Bf,Fno. (F-number), and angle 2ω of view (same for Tables 2 through 6,which will be described later).

Further, the middle section of Table 1 shows variable distance 1 (adistance between the first lens group G₁ and the second lens group G₂),variable distance 2 (a distance between the third lens group G₃ and thefourth lens group G₄), and variable distance 3 (a distance between thefourth lens group G₄ and the fifth lens group G₅) at a wide angle end(wide) and at a telephoto end (tele) (same for Tables 2 through 6, whichwill be described later). Further, the bottom section of Table 1 showsthe values of coefficients K, A₃ through A₁₀ corresponding to eachaspheric surface (same for Tables 2 through 6, which will be describedlater).

TABLE 1 f = 19.28~23.14, Bf = 26.53, Fno = 2.0~2.2, 2ω = 56.4°~48.4°ABBE SURFACE CURVATURE DISTANCE REFRACTIVE NUMBER NUMBERS OF RADIUS R DINDEX N_(d) ν_(d) *1 −505.465 3.30 1.491000 57.6 *2 228.339 6.00 3−360.055 1.50 1.487490 70.5 4 17.190 D1 5 41.315 2.69 1.772500 49.6 6−159.515 11.40 7 ∞(STOP) 14.98 8 6819.474 2.87 1.713000 53.9 9 −35.618D2 10 −24.429 1.00 1.761820 26.6 11 50.961 1.74 12 −80.651 4.06 1.71300053.9 13 −38.386 0.20 14 53.722 5.10 1.603110 60.6 15 −51.070 D3 1640.284 5.98 1.603110 60.6 17 ∞ 9.40 18 ∞ 26.00 1.516330 64.1 19 ∞PROJECTION DISTANCE 1.8 m inf D1 (WIDE ANGLE 26.73 26.25 END) D2 (WIDEANGLE  2.09  2.09 END) D3 (WIDE ANGLE  1.40  1.40 END) D1 (TELEPHOTO19.84 19.37 END) D2 (TELEPHOTO  5.59  5.59 END) D3 (TELEPHOTO  4.79 4.79 END) ASPHERIC COEFFICIENT FIRST SURFACE SECOND SURFACE κ−1.7620037E+03 −1.0512480E+04 A₃ 0.0000000E+00 0.0000000E+00 A₄1.3719124E−05 1.6303474E−04 A₅ 2.4610669E−05 −1.3420518E−05 A₆−4.1057965E−06 1.0043368E−06 A₇ 3.0940196E−07 −1.0977478E−07 A₈−1.0868151E−08 1.1220476E−08 A₉ 1.0507902E−10 −6.0191177E−10 A₁₀2.1134006E−12 1.2789507E−11 *ASPHERIC SURFACE

Further, Table 6 shows numerical values corresponding to theaforementioned formulas in Example 1.

FIGS. 6Ai, 6Aii, 6Aiii and 6Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 1 at a wide angle end (WIDE). FIGS. 6Bi, 6Bii, 6Biii and 6Bivare diagrams illustrating various aberrations (spherical aberration,astigmatism, distortion, and lateral chromatic aberration, respectively)of the zoom lens for projection in Example 1 at a telephoto end (TELE).FIGS. 7 i, 7 ii, 7 iii, 7 iv and 7 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 1 at a wide angleend (WIDE). FIGS. 8 i, 8 ii, 8 iii, 8 iv and 8 v are diagramsillustrating coma aberrations of the zoom lens for projection in Example1 at a telephoto end (TELE). In FIGS. 6Ai through 6Aiv and 6Bi through6Biv, and in FIGS. 9Ai through 9Aiv and 9Bi through 9Biv, FIGS. 12Aithrough 12Aiv and 12Bi through 12Biv, FIGS. 15Ai through 15Aiv and 15Bithrough 15Biv, and FIGS. 18Ai through 18Aiv and 18Bi through 18Biv,which will be described later, diagrams of spherical aberrationsillustrate aberrations for light with wavelengths of 550 nm, 460 nm, and620 nm. Further, diagrams of astigmatism illustrate aberrations withrespect to a sagittal image plane and a tangential image plane. Further,diagrams of lateral chromatic aberrations illustrate aberrations forlight with wavelengths of 460 nm and 620 nm with respect to light with awavelength of 550 nm.

As FIGS. 6Ai through 8 v clearly illustrate, the zoom lens forprojection in Example 1 has angle 2ω of view of 56.4 degrees, which iswide, at a wide angle end. Further, F-number is 2.0, which means thezoom lens is a fast lens. Further, various aberrations are corrected inan excellent manner.

Further, as Table 6 shows, the zoom lens for projection in Example 1satisfies the formulas (1) through (8), (1′), (4′) through (8′), (1″),(5″), (7″) and (8″).

Example 2

FIG. 2 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 2. The structure of the zoom lens forprojection in Example 2 is substantially the same as the structure ofthe zoom lens for projection in Example 1.

Table 2 shows the radius of curvature R (mm) of each lens surface inExample 2, the center thickness of each lens and air space betweenlenses D (mm), and refractive index N_(d) and the Abbe number ν_(d) ofeach lens for d-line.

TABLE 2 f = 19.24~23.08, Bf = 26.53, Fno = 2.0~2.2, 2ω = 56.8°~48.6°ABBE SURFACE CURVATURE DISTANCE REFRACTIVE NUMBER NUMBERS OF RADIUS R DINDEX N_(d) ν_(d) *1 −207.390 3.30 1.491000 57.6 *2 116.869 6.00 3−231.524 1.50 1.487490 70.5 4 17.977 D1 5 43.672 3.00 1.804000 46.6 6−134.308 13.80 7 ∞(STOP) 14.16 8 229.055 3.11 1.772500 49.6 9 −34.782 D210 −26.582 1.00 1.805180 25.5 11 48.234 1.77 12 −84.316 3.56 1.65160058.4 13 −39.206 0.20 14 50.922 5.22 1.603110 60.6 15 −53.033 D3 1650.066 4.62 1.772500 49.6 17 ∞ 9.40 18 ∞ 26.00 1.516330 64.1 19 ∞PROJECTION DISTANCE 1.8 m inf D1 (WIDE ANGLE 19.75 19.36 END) D2 (WIDEANGLE  1.84  1.84 END) D3 (WIDE ANGLE  2.87  2.87 END) D1 (TELEPHOTO13.27 12.88 END) D2 (TELEPHOTO  5.78  5.78 END) D3 (TELEPHOTO  5.42 5.42 END) ASPHERIC COEFFICIENT FIRST SURFACE SECOND SURFACE κ6.8213016E+01 −1.9372647E+03 A₃ 0.0000000E+00 0.0000000E+00 A₄2.0178895E−05 2.2171121E−04 A₅ 2.6731485E−05 −1.8938151E−05 A₆−4.3101145E−06 1.1561858E−06 A₇ 3.0912949E−07 −8.6677277E−08 A₈−1.0593519E−08 8.1802045E−09 A₉ 1.1801826E−10 −4.6195734E−10 A₁₀1.2731821E−12 1.0731464E−11 *ASPHERIC SURFACE

Further, Table 6 shows numerical values corresponding to theaforementioned formulas in Example 2.

FIGS. 9Ai, 9Aii, 9Aiii and 9Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 2 at a wide angle end (WIDE). FIGS. 9Bi, 9Bii, 9Biii and 9Bivare diagrams illustrating various aberrations (spherical aberration,astigmatism, distortion, and lateral chromatic aberration, respectively)of the zoom lens for projection in Example 2 at a telephoto end (TELE).FIGS. 10 i, 10 ii, 10 iii, 10 iv and 10 v are diagrams illustrating comaaberrations of the zoom lens for projection in Example 2 at a wide angleend (WIDE). FIGS. 11 i, 11 ii, 11 iii, 11 iv and 11 v are diagramsillustrating coma aberrations of the zoom lens for projection in Example2 at a telephoto end (TELE).

As FIGS. 9Ai through 11 v clearly illustrate, the zoom lens forprojection in Example 2 has angle 2ω of view of 56.8 degrees, which iswide, at a wide angle end. Further, F-number is 2.0, which means thezoom lens is a fast lens. Further, various aberrations are corrected inan excellent manner.

Further, as Table 6 shows, the zoom lens for projection in Example 2satisfies the formulas (1) through (8), (1′), (4′) through (8′), (1″),(5″), (7″) and (8″).

Example 3

FIG. 3 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 3. The structure of the zoom lens forprojection in Example 3 is substantially the same as the structure ofthe zoom lens for projection in Example 1.

Table 3 shows the radius of curvature R (mm) of each lens surface inExample 3, the center thickness of each lens and air space betweenlenses D (mm), and refractive index N_(d) and the Abbe number ν_(d) ofeach lens for d-line.

TABLE 3 f = 19.23~23.07, Bf = 26.53, Fno = 2.0~2.2, 2ω = 56.4°~48.2°ABBE SURFACE CURVATURE DISTANCE REFRACTIVE NUMBER NUMBERS OF RADIUS R DINDEX N_(d) ν_(d) *1 −1004.556 3.30 1.491000 57.6 *2 149.556 5.47 3−193.403 1.50 1.487490 70.5 4 16.117 D1 5 40.485 3.03 1.772500 49.6 6−117.131 12.95 7 ∞(STOP) 13.53 8 255.797 3.07 1.713000 53.9 9 −31.957 D210 −24.029 1.00 1.761820 26.6 11 48.535 2.04 12 −59.303 4.18 1.71300053.9 13 −33.383 0.20 14 49.993 5.04 1.603110 60.6 15 −54.026 D3 1642.929 5.10 1.603110 60.6 17 ∞ 9.40 18 ∞ 26.00 1.516330 64.1 19 ∞PROJECTION DISTANCE 1.8 m inf D1 (WIDE ANGLE 19.81 19.42 END) D2 (WIDEANGLE  1.89  1.89 END) D3 (WIDE ANGLE  0.30  0.30 END) D1 (TELEPHOTO13.53 13.14 END) D2 (TELEPHOTO  5.75  5.75 END) D3 (TELEPHOTO  2.72 2.72 END) ASPHERIC COEFFICIENT FIRST SURFACE SECOND SURFACE κ−9.6872740E+03 −4.2145832E+03 A₃ 0.0000000E+00 0.0000000E+00 A₄9.0728410E−06 1.8341354E−04 A₅ 2.7015636E−05 −1.4609365E−05 A₆−4.3088183E−06 9.5801488E−07 A₇ 3.0895978E−07 −1.0971530E−07 A₈−1.0597122E−08 1.1078358E−08 A₉ 1.2616519E−10 −5.5073312E−10 A₁₀7.8581631E−13 1.0038880E−11 *ASPHERIC SURFACE

Further Table 6 shows numerical values corresponding to theaforementioned formulas in Example 3.

FIGS. 12Ai, 12Aii, 12Aiii and 12Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 3 at a wide angle end (WIDE). FIGS. 12Bi, 12Bii, 12Biii and12Biv are diagrams illustrating various aberrations (sphericalaberration, astigmatism, distortion, and lateral chromatic aberration,respectively) of the zoom lens for projection in Example 3 at atelephoto end (TELE). FIGS. 13 i, 13 ii, 13 iii, 13 iv and 13 v arediagrams illustrating coma aberrations of the zoom lens for projectionin Example 3 at a wide angle end (WIDE). FIGS. 14 i, 14 ii, 14 iii, 14iv and 14 v are diagrams illustrating coma aberrations of the zoom lensfor projection in Example 3 at a telephoto end (TELE).

As FIGS. 12Ai through 14 v clearly illustrate, the zoom lens forprojection in Example 3 has angle 2ω of view of 56.4 degrees, which iswide, at a wide angle end. Further, F-number is 2.0, which means thezoom lens is a fast lens. Further, various aberrations are corrected inan excellent manner.

Further, as Table 6 shows, the zoom lens for projection in Example 3satisfies the formulas (1) through (8), (1′), (4′) through (8′), (1″),(5″), (7″) and (8″).

Example 4

FIG. 4 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 4. The structure of the zoom lens forprojection in Example 4 is substantially the same as the structure ofthe zoom lens for projection in Example 3.

Table 4 shows the radius of curvature R (mm) of each lens surface inExample 4, the center thickness of each lens and air space betweenlenses D (mm), and refractive index N_(d) and the Abbe number ν_(d) ofeach lens for d-line.

TABLE 4 f = 19.23~23.07, Bf = 26.53, Fno = 2.0~2.2, 2ω = 56.4°~48.8°ABBE SURFACE CURVATURE DISTANCE REFRACTIVE NUMBER NUMBERS OF RADIUS R DINDEX N_(d) ν_(d) *1 −278.832 3.30 1.491000 57.6 *2 107.895 6.00 3−193.634 1.50 1.487490 70.5 4 17.525 D1 5 43.400 2.91 1.804000 46.6 6−126.361 14.70 7 ∞(STOP) 13.28 8 201.278 2.88 1.772500 49.6 9 −35.488 D210 −26.427 1.00 1.805180 25.5 11 47.016 1.83 12 −80.491 4.33 1.65160058.4 13 −38.243 0.20 14 50.665 5.03 1.603110 60.6 15 −52.649 D3 1652.241 4.67 1.772500 49.6 17 ∞ 9.40 18 ∞ 26.00 1.516330 64.1 19 ∞PROJECTION DISTANCE 1.8 m inf D1 (WIDE ANGLE 19.97 19.60 END) D2 (WIDEANGLE  1.84  1.84 END) D3 (WIDE ANGLE  3.47  3.47 END) D1 (TELEPHOTO13.51 13.14 END) D2 (TELEPHOTO  5.81  5.81 END) D3 (TELEPHOTO  5.96 5.96 END) ASPHERIC COEFFICIENT FIRST SURFACE SECOND SURFACE κ−2.4365795E+02 −1.6780505E+03 A₃ 0.0000000E+00 0.0000000E+00 A₄2.1552841E−05 2.3368610E−04 A₅ 2.6828305E−05 −2.0138680E−05 A₆−4.3609858E−06 1.1824020E−06 A₇ 3.0986776E−07 −8.4953727E−08 A₈−1.0318899E−08 7.5546931E−09 A₉ 1.0364030E−10 −3.9020287E−10 A₁₀1.4210073E−12 8.0244434E−12 *ASPHERIC SURFACE

Further, Table 6 shows numerical values corresponding to theaforementioned formulas in Example 4.

FIGS. 15Ai, 15Aii, 15Aiii and 15Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 4 at a wide angle end (WIDE). FIGS. 15Bi, 15Bii, 15Biii and15Biv are diagrams illustrating various aberrations (sphericalaberration, astigmatism, distortion, and lateral chromatic aberration,respectively) of the zoom lens for projection in Example 4 at atelephoto end (TELE). FIGS. 16 i, 16 ii, 16 iii, 16 iv and 16 v arediagrams illustrating coma aberrations of the zoom lens for projectionin Example 4 at a wide angle end (WIDE). FIGS. 17 i, 17 ii, 17 iii, 17iv and 17 v are diagrams illustrating coma aberrations of the zoom lensfor projection in Example 4 at a telephoto end (TELE).

As FIGS. 15Ai through 17 v clearly illustrate, the zoom lens forprojection in Example 4 has angle 2ω of view of 56.4 degrees, which iswide, at a wide angle end. Further, F-number is 2.0, which means thezoom lens is a fast lens. Further, various aberrations are corrected inan excellent manner.

Further, as Table 6 shows, the zoom lens for projection in Example 4satisfies the formulas (1) through (8), (1′), (4′) through (8′), (1″),(5″), (7″) and (8″).

Example 5

FIG. 5 is a schematic diagram illustrating the structure of a zoom lensfor projection in Example 5. The structure of the zoom lens forprojection in Example 5 is substantially the same as the structure ofthe zoom lens for projection in Example 1. However, the zoom lens forprojection in Example 5 differs from Example 1 in that the fourth lensgroup G₄ has positive refractive power.

Table 5 shows the radius of curvature R (mm) of each lens surface inExample 5, the center thickness of each lens and air space betweenlenses D (mm), and refractive index N_(d) and the Abbe number ν_(d) ofeach lens for d-line.

TABLE 5 f = 19.28~23.13, Bf = 26.52, Fno = 2.0~2.3, 2ω = 56.4°~48.2°ABBE SURFACE CURVATURE DISTANCE REFRACTIVE NUMBER NUMBERS OF RADIUS R DINDEX N_(d) ν_(d) *1 −100.201 3.30 1.491000 57.6 *2 2727.353 6.00 3−200.448 1.50 1.487490 70.5 4 18.802 D1 5 35.473 3.90 1.772500 49.6 6−147.682 19.45 7 ∞(STOP) 6.20 8 295.201 2.29 1.713000 53.9 9 −37.058 D210 −16.662 1.00 1.761820 26.6 11 46.266 1.97 12 −51.355 3.14 1.71300053.9 13 −30.724 2.13 14 114.682 7.14 1.603110 60.6 15 −23.048 D3 1640.818 5.06 1.603110 60.6 17 ∞ 9.40 18 ∞ 26.00 1.516330 64.1 19 ∞PROJECTION DISTANCE 1.8 m inf D1 (WIDE ANGLE 23.18 22.74 END) D2 (WIDEANGLE  2.63  2.63 END) D3 (WIDE ANGLE  1.33  1.33 END) D1 (TELEPHOTO16.30 15.85 END) D2 (TELEPHOTO  5.99  5.99 END) D3 (TELEPHOTO  4.86 4.86 END) ASPHERIC COEFFICIENT FIRST SURFACE SECOND SURFACE κ0.0000000E+00 0.0000000E+00 A₃ −1.0594101E−03 −1.2836607E−03 A₄2.2664791E−04 3.0461114E−04 A₅ 1.5444042E−06 −1.3813852E−05 A₆−2.4215745E−06 −2.0334357E−07 A₇ 2.2779591E−07 −1.1434813E−09 A₈−9.5910974E−09 6.0083755E−09 A₉ 1.8249323E−10 −4.1481971E−10 A₁₀−1.0203913E−12 8.4638822E−12 *ASPHERIC SURFACE

Further, Table 6 shows numerical values corresponding to theaforementioned formulas in Example 5.

FIGS. 18Ai, 18Aii, 18Aiii and 18Aiv are diagrams illustrating variousaberrations (spherical aberration, astigmatism, distortion, and lateralchromatic aberration, respectively) of the zoom lens for projection inExample 5 at a wide angle end (WIDE). FIGS. 18Bi, 18Bii, 18Biii and18Biv are diagrams illustrating various aberrations (sphericalaberration, astigmatism, distortion, and lateral chromatic aberration,respectively) of the zoom lens for projection in Example 5 at atelephoto end (TELE). FIGS. 19 i, 19 ii, 19 iii, 19 iv and 19 v arediagrams illustrating coma aberrations of the zoom lens for projectionin Example 5 at a wide angle end (WIDE). FIGS. 20 i, 20 ii, 20 iii, 20iv and 20 v are diagrams illustrating coma aberrations of the zoom lensfor projection in Example 5 at a telephoto end (TELE).

As FIGS. 18Ai through 20 v clearly illustrate, the zoom lens forprojection in Example 5 has angle 2ω of view of 56.4 degrees, which iswide, at a wide angle end. Further, F-number is 2.0, which means thezoom lens is a fast lens. Further, various aberrations are corrected inan excellent manner.

Further, as Table 6 shows, the zoom lens for projection in Example 5satisfies the formulas (2) through (5), (7), (8), (4′), (7′), (8′), (7″)and (8″).

TABLE 6 FORMULA EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 EXAMPLE 5 (1),(1′), (1″), (R₇₂ + R₇₁)/ −0.03 0.02 0.04 0.02 −0.67 (2) (R₇₂ − R₇₁) (3)f₄/f₅ −3.62 −2.42 −3.46 −2.71 922.68 (4), (4′), fn/fw −3.68 −3.46 −3.15−3.35 −2.87 (8), (8′), (8″) (5), (5′), (5″) f₄/f₂ −5.66 −3.81 −6.28−4.53 1671.98 (6), (6′) f₄/fw −12.50 −8.13 −12.77 −9.48 3226.03 (7),(7′), (7″), |f_(1A)/fw| 16.52 7.85 13.72 8.18 10.16

1. A zoom lens for projection comprising: a first lens group havingnegative refractive power, and which is composed of two lenses; a secondlens group composed of a positive lens; an aperture stop; a third lensgroup composed of a positive lens; a fourth lens group composed of threelenses of a fourth-group-first lens, which is a negative lens, afourth-group-second lens arranged in such a manner that a negative airlens is formed between the fourth-group-first lens and thefourth-group-second lens, and a fourth-group-third lens, which is apositive lens, and the fourth-group-first lens, the fourth-group-secondlens and the fourth-group-third lens being arranged in this order fromthe magnification side of the zoom lens; and a fifth lens group composedof a positive lens having a convex surface facing the magnificationside, and the first lens group, the second lens group, the aperturestop, the third lens group, the fourth lens group, and the fifth lensgroup being arranged from the magnification side in the order mentionedabove, wherein the following formula (1) is satisfied:−0.6<(R ₇₂ +R ₇₁)/(R ₇₂ −R ₇₁)<0.6  (1), where R₇₁ is a radius ofcurvature of a magnification-side surface of the fourth-group-thirdlens, and R₇₂ is a radius of curvature of a reduction-side surface ofthe fourth-group-third lens.
 2. A zoom lens for projection comprising: afirst lens group having negative refractive power, and which is composedof two lenses; a second lens group composed of a positive lens; anaperture stop; a third lens group composed of a positive lens; a fourthlens group composed of three lenses of a fourth-group-first lens, whichis a negative lens, a fourth-group-second lens arranged in such a mannerthat a negative air lens is formed between the fourth-group-first lensand the fourth-group-second lens, and a fourth-group-third lens, whichis a positive lens, and the fourth-group-first lens, thefourth-group-second lens and the fourth-group-third lens being arrangedin this order from the magnification side of the zoom lens; and a fifthlens group composed of a positive lens having a convex surface facingthe magnification side, and the first lens group, the second lens group,the aperture stop, the third lens group, the fourth lens group, and thefifth lens group being arranged from the magnification side in the ordermentioned above, wherein the following formulas (2) and (3) aresatisfied:−0.85<(R ₇₂ +R ₇₁)/(R ₇₂ −R ₇₁)<0.85  (2); and−6.0<f ₄ /f ₅  (3), where R₇₁ is a radius of curvature of amagnification-side surface of the fourth-group-third lens, R₇₂ is aradius of curvature of a reduction-side surface of thefourth-group-third lens, f₄ is a focal length of the fourth lens group,and f₅ is a focal length of the fifth lens group.
 3. A zoom lens forprojection comprising: a first lens group having negative refractivepower, and which is composed of two lenses; a second lens group composedof a positive lens; an aperture stop; a third lens group composed of apositive lens; a fourth lens group composed of three lenses of afourth-group-first lens, which is a negative lens, a fourth-group-secondlens arranged in such a manner that a negative air lens is formedbetween the fourth-group-first lens and the fourth-group-second lens,and a fourth-group-third lens, which is a positive lens, and thefourth-group-first lens, the fourth-group-second lens and thefourth-group-third lens being arranged in this order from themagnification side of the zoom lens; and a fifth lens group composed ofa positive lens having a convex surface facing the magnification side,and the first lens group, the second lens group, the aperture stop, thethird lens group, the fourth lens group, and the fifth lens group beingarranged from the magnification side in the order mentioned above,wherein the following formulas (4) and (5) are satisfied:−6.0<fn/fw<−2.0  (4); and−11.0<f ₄ /f ₂  (5), where fn is a focal length of the negative airlens, fw is a focal length of the entire system of the zoom lens at awide angle end, f₂ is a focal length of the second lens group, and f₄ isa focal length of the fourth lens group.
 4. zoom lens for projectioncomprising: a first lens group having negative refractive power, andwhich is composed of two lenses; a second lens group composed of apositive lens; an aperture stop; a third lens group composed of apositive lens; a fourth lens group composed of three lenses of afourth-group-first lens, which is a negative lens, a fourth-group-secondlens arranged in such a manner that a negative air lens is formedbetween the fourth-group-first lens and the fourth-group-second lens,and a fourth-group-third lens, which is a positive lens, and thefourth-group-first lens, the fourth-group-second lens and thefourth-group-third lens being arranged in this order from themagnification side of the zoom lens; and a fifth lens group composed ofa positive lens having a convex surface facing the magnification side,and the first lens group, the second lens group, the aperture stop, thethird lens group, the fourth lens group, and the fifth lens group beingarranged from the magnification side in the order mentioned above,wherein the following formula (6) is satisfied:−24.0<f ₄ /fw<−6.0  (6), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and f₄ is a focal length of thefourth lens group.
 5. A zoom lens for projection, as defined in claim 1,wherein at least a surface of the magnification-side lens of the twolenses in the first lens group is aspheric, and wherein thereduction-side lens of the two lenses in the first lens group has aconcave surface facing the reduction side of the zoom lens, and whereinthe positive lens in the second lens group has a convex surface facingthe magnification side, and wherein the positive lens in the third lensgroup has a convex surface facing the magnification side, and whereinthe fourth-group-first lens of the three lenses in the fourth lens grouphas a concave surface facing the magnification side, and wherein thefourth-group-third lens of the three lenses in the fourth lens group hasa convex surface facing the reduction side.
 6. A zoom lens forprojection, as defined in claim 2, wherein at least a surface of themagnification-side lens of the two lenses in the first lens group isaspheric, and wherein the reduction-side lens of the two lenses in thefirst lens group has a concave surface facing the reduction side of thezoom lens, and wherein the positive lens in the second lens group has aconvex surface facing the magnification side, and wherein the positivelens in the third lens group has a convex surface facing themagnification side, and wherein the fourth-group-first lens of the threelenses in the fourth lens group has a concave surface facing themagnification side, and wherein the fourth-group-third lens of the threelenses in the fourth lens group has a convex surface facing thereduction side.
 7. A zoom lens for projection, as defined in claim 3,wherein at least a surface of the magnification-side lens of the twolenses in the first lens group is aspheric, and wherein thereduction-side lens of the two lenses in the first lens group has aconcave surface facing the reduction side of the zoom lens, and whereinthe positive lens in the second lens group has a convex surface facingthe magnification side, and wherein the positive lens in the third lensgroup has a convex surface facing the magnification side, and whereinthe fourth-group-first lens of the three lenses in the fourth lens grouphas a concave surface facing the magnification side, and wherein thefourth-group-third lens of the three lenses in the fourth lens group hasa convex surface facing the reduction side.
 8. A zoom lens forprojection, as defined in claim 4, wherein at least a surface of themagnification-side lens of the two lenses in the first lens group isaspheric, and wherein the reduction-side lens of the two lenses in thefirst lens group has a concave surface facing the reduction side of thezoom lens, and wherein the positive lens in the second lens group has aconvex surface facing the magnification side, and wherein the positivelens in the third lens group has a convex surface facing themagnification side, and wherein the fourth-group-first lens of the threelenses in the fourth lens group has a concave surface facing themagnification side, and wherein the fourth-group-third lens of the threelenses in the fourth lens group has a convex surface facing thereduction side.
 9. A zoom lens for projection, as defined in claim 1,wherein the following formula (7) is satisfied:3.0<|f _(1A) /fw|  (7), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and f_(1A) is a focal length ofthe magnification-side lens in the first lens group.
 10. A zoom lens forprojection, as defined in claim 2, wherein the following formula (7) issatisfied:3.0<|f _(1A) /fw|  (7), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and f_(1A) is a focal length ofthe magnification-side lens in the first lens group.
 11. A zoom lens forprojection, as defined in claim 3, wherein the following formula (7) issatisfied:3.0<|f _(1A) /fw|  (7), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and f_(1A) is a focal length ofthe magnification-side lens in the first lens group.
 12. A zoom lens forprojection, as defined in claim 4, wherein the following formula (7) issatisfied:3.0<|f _(1A) /fw|  (7), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and f_(1A) is a focal length ofthe magnification-side lens in the first lens group.
 13. A zoom lens forprojection, as defined in claim 1, wherein the following formula (8) issatisfied:−20.0<fn/fw<−0.5  (8), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and fn is a focal length of thenegative air lens.
 14. A zoom lens for projection, as defined in claim2, wherein the following formula (8) is satisfied:−20.0<fn/fw<−0.5  (8), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and fn is a focal length of thenegative air lens.
 15. A zoom lens for projection, as defined in claim3, wherein the following formula (8) is satisfied:−20.0<fn/fw<−0.5  (8), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and fn is a focal length of thenegative air lens.
 16. A zoom lens for projection, as defined in claim4, wherein the following formula (8) is satisfied:−20.0<fn/fw<−0.5  (8), where fw is a focal length of the entire systemof the zoom lens at a wide angle end, and fn is a focal length of thenegative air lens.
 17. A projection-type display apparatus comprising: alight source; a light valve; an illumination optical system that guidesrays of light output from the light source to the light valve; and azoom lens for projection, as defined in claim 1, wherein the light valveoptically modulates the rays of light output from the light source, andwherein the zoom lens for projection projects the modulated rays oflight onto a screen.
 18. A projection-type display apparatus comprising:a light source; a light valve; an illumination optical system thatguides rays of light output from the light source to the light valve;and a zoom lens for projection, as defined in claim 2, wherein the lightvalve optically modulates the rays of light output from the lightsource, and wherein the zoom lens for projection projects the modulatedrays of light onto a screen.
 19. A projection-type display apparatuscomprising: a light source; a light valve; an illumination opticalsystem that guides rays of light output from the light source to thelight valve; and a zoom lens for projection, as defined in claim 3,wherein the light valve optically modulates the rays of light outputfrom the light source, and wherein the zoom lens for projection projectsthe modulated rays of light onto a screen.
 20. A projection-type displayapparatus comprising: a light source; a light valve; an illuminationoptical system that guides rays of light output from the light source tothe light valve; and a zoom lens for projection, as defined in claim 4,wherein the light valve optically modulates the rays of light outputfrom the light source, and wherein the zoom lens for projection projectsthe modulated rays of light onto a screen.